The present invention related to circuit breakers for use in electrical circuits. More particularly. the invention relates to a system for automatically discharging the capacitor of a magnetically or electrically-actuated circuit breaker upon removal of the circuit breaker from its enclosure.
Magnetic and electrically-actuated circuit breakers typically comprise one or more capacitors that store electrical energy in the form of an electric field. The electrical energy is used to energize the coils of an actuator mechanism that opens and closes the contact of the circuit breaker. The electric field within the capacitor of a power circuit breaker can have a magnitude of one farad or greater. Electrical fields of this magnitude can cause serious injury or death to personnel exposed to the electrical field. For example, maintenance personnel removing a circuit breaker from its enclosure for service or replacement can easily be exposed to the electrical field stored in circuit breaker""s capacitors if adequate safety measures are not observed. Hence, regulatory authorities often require some type of safeguard against such exposure. For example, American National Standards Institute (ANSI) C37.20.2 requires that magnetic and electrically-actuated circuit breakers have some type of mechanism that automatically discharges the stored energy of the circuit breaker""s capacitors before or during removal of the circuit breaker from its enclosure.
Medium-voltage circuit breakers are often housed in relatively compact switchgear enclosures. Hence, any safety-related measure added to such a circuit breaker must not cause the dimensions of the circuit breaker to exceed those of its enclosure. Furthermore, minimizing the cost and complexity of a particular safety measure encourages adoption of the safety measure, and therefore is particularly desirable.
A need therefore exists for a simple, compact, and inexpensive system for automatically discharging the capacitor of a circuit breaker upon removal of the circuit breaker from its housing or enclosure.
A presently-preferred embodiment of a circuit breaker adapted to be installed in a switchgear enclosure comprises a support truck comprising a longitudinally-oriented member, a laterally-oriented member fixedly coupled the longitudinally-oriented member, and a wheel rotatably coupled to the laterally-oriented member. The circuit breaker also comprises a contact mechanism fixedly coupled to the support truck and comprising a first and a second contact member. The circuit breaker further comprises an actuator mechanism comprising a coil, a capacitor adapted to energize the coil on a selective basis, and an armature mechanically coupled to the second contact member and adapted to urge the second contact member into electrical contact with the first contact member in response to energization of the coil.
The circuit breaker also comprises a racking mechanism adapted to move the support truck in relation to the switchgear enclosure. The racking mechanism comprises a channel member and a locking arm mechanically coupled to the channel member and movable between a locked position wherein the locking arm is adapted to engage a slot on the switchgear enclosure, and an unlocked position wherein the locking arm is disengaged from the slot.
The circuit breaker further comprises a capacitor discharge system comprising a switch lever rigidly coupled to the locking arm, a capacitor discharge circuit, a contact switch mechanically coupled to the support truck and movable between an open and a closed position, a resistor electrically coupled to the capacitor discharge circuit and the capacitor, and a relay electrically coupled to the capacitor discharge circuit, the capacitor, and the resistor. The switch lever is adapted to move the contact switch from the open to the closed position when the locking arm is moved from the locked to the unlocked position, and the capacitor discharge circuit is adapted to energize the relay when the contact switch is moved to the closed position thereby establishing electrical contact between the capacitor and the resistor.
A presently-preferred embodiment of a circuit breaker adapted for use in a switchgear enclosure comprises a support truck adapted to translate in relation of the switchgear enclosure, and a first and a second contact member mounted on the support truck. The circuit breaker also comprises a coil, a capacitor adapted to energize the coil, and an armature adapted to move the second contact member in response to energization of the coil. The circuit breaker further comprises a racking mechanism comprising a locking arm movable between a locked position wherein the locking arm is adapted to engage the switchgear enclosure, and an unlocked position wherein the locking arm is disengaged from the switchgear enclosure.
The circuit breaker also comprises a capacitor discharge system comprising a capacitor discharge circuit electrically coupled to the capacitor, and a contact switch mechanically coupled to the support truck and electrically coupled to the capacitor discharge circuit and being movable between a first and a second position. The capacitor discharge system also comprises a resistor electrically coupled to the capacitor discharge circuit, and a lever arm rigidly coupled to the locking arm and adapted to move the contact switch from the first to the second position when the locking arm is moved from the locked to the unlocked position. The capacitor discharge system is adapted to electrically couple the capacitor and the resistor when the contact switch is in the second position.
Another presently-preferred embodiment of a circuit breaker adapted for use in a switchgear enclosure comprises a support truck, a contact member mounted on the support truck, and a coil. The circuit breaker also comprises a capacitor adapted to energize the coil, and an armature adapted to move the contact member in response to energization of the coil.
The circuit breaker also comprises a racking mechanism adapted to move the support truck in relation to the switchgear enclosure and comprising a locking arm movable between a locked position wherein the locking arm is adapted to engage the switchgear enclosure, and an unlocked position wherein the locking arm is disengaged from the switchgear enclosure.
The circuit breaker also comprises a capacitor discharge system comprising a resistor and a capacitor discharge circuit adapted to electrically couple the capacitor and the resistor in response to movement of the locking arm from the locked to the unlocked positions.
A presently-preferred system for automatically discharging a capacitor of a circuit breaker adapted for use in a switchgear enclosure comprises a capacitor discharge circuit adapted to be electrically coupled to the capacitor, and a contact switch electrically coupled to the capacitor discharge circuit and adapted to be mechanically coupled to a support truck of the circuit breaker. The contact switch is movable between a first and a second position. The system also comprises a resistor electrically coupled to the capacitor discharge circuit, and a lever arm adapted to be rigidly coupled to a racking mechanism of the circuit breaker and adapted to urge the contact switch into the closed position when a locking arm of the racking mechanism disengages from the switchgear enclosure. The capacitor discharge system is adapted to electrically couple the capacitor and the resistor when the contact switch is in the second position thereby discharging the capacitor.
A presently-preferred method of removing a circuit breaker from a switchgear enclosure to minimize a possibility of personnel injury caused by contact with a capacitor of the circuit breaker comprises disengaging a locking handle of the circuit breaker from the switchgear enclosure and moving a contact switch of the circuit breaker to a closed position to establish electrical contact between the capacitor and a resistor by moving the locking handle from a locked to an unlocked position. The method also comprises applying a force to the circuit breaker to urge the circuit breaker out of the switchgear enclosure.